1. Field of the Invention
The present invention relates to a power circuit including a low temperature polysilicon thin film transistor provided on an insulating substrate, an active matrix-type display device such as a liquid crystal display device, and a mobile terminal containing the power circuit and the display device.
2. Description of Related Art
Recently, mobile terminals such as cellular phones and PDAs (personal digital assistants) have become increasingly widespread. One reason for this rapid spread of the mobile terminal is the development of a liquid crystal display device mounted on the mobile terminal as an output display unit. The liquid crystal display device contributes to the wide spread of the mobile terminal because this display device is a low power consumption type display device having characteristics of requiring substantially no driving power in principle.
Currently, the number of such an active matrix type display device has been increasing, which uses polysilicon TFTs (thin film transistors) as switching elements for pixels, and has a digital interface driving circuit on the same substrate as that of a display area containing pixels arranged in a matrix. In this structure, the digital interface driving circuit is provided integrally with the display area.
In this driving circuit integrated type display device, a horizontal driving system and a vertical driving system are disposed on a peripheral area (frame) of an active display unit. These driving systems using the low temperature polysilicon TFTs are formed integrally with the pixel area on the same substrate.
FIG. 1 illustrates a general structure of a typical driving circuit integrated type display device (for example, see JP-A-2002-175033).
As illustrated in FIG. 1, this liquid crystal display device integrates an active display unit 2 where plural pixels including liquid crystal cells are disposed in a matrix, a pair of horizontal driving circuits (H drivers) 3U and 3D positioned above and below the active display unit 2 in FIG. 1, a vertical driving circuit (V driver) 4 disposed on one side of the active display unit 2 in FIG. 1, a reference voltage generating circuit 5 for generating plural reference voltages, a data processing circuit 6, and other parts, all of which components are provided on a transparent insulating substrate such as a glass substrate 1.
As can be seen from the figure, the driving circuit integrated type display device shown in FIG. 1 has the two horizontal driving circuits 3U and 3D disposed on both the sides of the active pixel unit 2 (above and below in FIG. 1) so as to separately drive odd lines and even lines of data lines.
FIG. 2 is a block diagram showing a structure example of the horizontal driving circuits 3U and 3D shown in FIG. 1 for separately driving odd lines and even lines.
As shown in FIG. 2, the horizontal driving circuit 3U for driving odd lines and the horizontal driving circuit 3D for driving even lines have the same structure.
More specifically, each of the horizontal driving circuits 3U and 3D has a shift register (HSR) group 3HSRU or 3HSRD for sequentially outputting a shift pulse (sampling pulse) from each transfer channel in synchronization with a horizontal transfer clock HCK (not shown), a sampling latch circuit group 3SMPLU or 3SMPLD for sequentially sampling and latching digital image data according to a sampling pulse given from shift registers 31U or 31D, a linearly sequential processing latch circuit group 3LTCU or 3LTCD for executing linearly sequential processing for the respective latch data from sampling latch circuits 32U or 32D, and a digital/analog converting circuit (DAC) group 3DACU or 3DACD for converting the digital image data obtained after linearly sequential processing by linearly sequential processing latch circuits 33U or 33D into analog image signals.
Generally, a level shift circuit is disposed on each input channel of DACs 34U and 34D so that level-raised data can be inputted to the DACs 34U and 34D.